544 



Miss E. R. Saunders. 



[Aug. 1, 



made as to the result as regards surface character of matings between 

 specified colours. Whether Fi from two glabrous parents (dissimilar in 

 colour or not) is all glabrous, or all hoary, or mixed, will depend upon the 

 particular constitution of the parents in each case, and to a knowledge of 

 this constitution, as we have seen, the colour of the flower is not in itself a 

 sufficient guide. Nor can we predict the exact proportion of the different 

 types in F 2 merely from a knowledge of the characters (colour and surface) 

 in Fi, since we are unable by inspection to tell whether the crossbred is 

 homozygous or heterozygous in respect of some of the effective factors, or 

 whether again one member of a pair may be present, but ineffective owing to 

 the absence of the complementary factor. We may, however, safely assert that 

 where two glabrous individuals give a glabrous Fi all the succeeding generations 

 will be glabrous. On the other hand, where such an Fi is hoary, F 2 will be 

 mixed hoary and glabrous, the proportion of the two forms depending upon 

 whether Fi is heterozygous in 2, 3, or all 4 factors (C, E, H, K). If F x is 

 heterozygous in only two of these factors we get a slight excess of hoary 

 plants in F 2 (9 hoary : 7 glabrous). If Fi is heterozygous in more than 

 two factors we shall expect the glabrous individuals to be more numerous 

 than the hoary. Other complications apart, the expectation will be 

 27 hoary : 37 glabrous when Fi is heterozygous in three factors, and 

 81 hoary : 175 glabrous when it is heterozygous in all four. 



We may now restate the main conclusions relating to surface character 

 and the appearance of colour in the sap as follows : — 



Summary of Conclusions. 



1. Sap-colour in Stocks is due to the presence of two factors (C and E), in 

 the absence of either or both of which the sap is colourless. 



2. Hoariness also depends upon the presence of two factors (H and K) 

 between which and the sap-colour pair a certain inter-relation may exist 

 (see 3). 



3. This inter-relationship between the two pairs of factors is such that 

 when certain strains are inter-crossed the hoary effect due to the presence 

 of the H, K pair is only manifested when the C, E pair is also present. 

 Hence a ?wm-sap-coloured individual may contain both H and K and yet be 

 glabrous, but in a s«j?-coloured glabrous form H and K cannot both be 

 present. One alone may occur, or both may be absent. 



4. Similarly a no?z,-sap-coloured glabrous form cannot contain both C and 

 E. Either alone may be present or both may be absent. 



5. Glabrous plants, whether alike in colour or not, when bred together, 

 will yield an Fi all hoary, or mixed hoary and glabrous, or all glabrous 



